This application claims the priority benefit of German patent application DE 101 10 993.8 filed on Mar. 7, 2001.
Not Applicable
The present invention relates to a device for detecting, monitoring and controlling the operating status of an electric iron or flat-iron. Commonly, the user is accustomed to receiving an optical signal, such as a light, indicating a supply of energy to a heating element of the electric iron. Usually, a glow lamp is used for this purpose, and the glow lamp, with a resistor connected in series therewith, is connected in parallel to the heating element.
Some commercially available steam irons furthermore comprise an electronic assembly which conducts and/or switches the heating current. Often, the electronic assembly is provided with additional optical or acoustic indicator means for indicating further characteristics of the operating status of the electric iron. The indicator means are controlled by a control unit provided in the electronic assembly which also comprises a low voltage power supply for energizing the additional indicator means and the control unit.
FIG. 1 shows a circuit diagram of a prior art steam iron which is provided with the above mentioned glow lamp indicator and an electronic assembly having additional indicator means. The circuitry comprises a so-called safety shut-off device such as, for example, implemented in a steam iron TDA 7550 of Bosch.
As shown in the circuit diagram of FIG. 1, the electronic assembly 1 comprises a low voltage power supply 2 which is energized by the line voltage supply L, N without galvanic isolation via an impedance 3 connected in series therewith. The low voltage power supply energizes a control unit 4 and a LED-indicator unit 5. The control unit 4 controls a power switch 6 which is a component of the electronic assembly 1, and is connected in series with an electric heating circuit L, 7, 10, N of the iron for opening the electric heating circuit.
The output of the control circuit 4 driving the power switch 6 is depending on delay timers (not shown), optionally in combination with a sensor system (not shown) for detecting different positions (upright, horizontal) and/or movements of the electric iron or flat iron. The present operating status of the electronic assembly 1 and, hence, of the iron, is displayed by indicator unit 5 which comprises a light-emitting diode providing an alarm indication by flashing when the power switch 6 has been opened by means of control unit 4 depending on the delay timers and/or the movement and position status sensor.
The electric heating circuit of the iron comprises a heating element 10 and a power switch 7 being connected in series therewith and constituting the primary ON/OFF-switch for the heating element 10. Power switch 7 is provided outside of the electronic assembly 1 and, for this reason, is called hereafter xe2x80x9cexternalxe2x80x9d power switch. The external power switch 7 corresponds to the thermostat at the iron sole and is switched (closed and opened) by the usual thermostat adjustment with a temperature sensor and a manually selectable temperature range.
The power switch 6 being integrated in the electronic assembly 1 and, for this reason, being called hereafter xe2x80x9cinternalxe2x80x9d power switch, allows a safety shut-off of the energized iron in addition to the thermostatically controlled ON/OFF-switching by means of external power switch 7. The safety shut-off is initiated a predetermined fixed time after an initial switch-on of the iron""s thermostat or when the above mentioned position and movement sensor system has not detected a movement of the iron over a predetermined time period. The above alarm indication within indicating unit 5 is exclusively given when the heating element current can no longer flow due to a forced shut-off of the heating element current by controlled opening of the internal power switch 6.
A glow lamp 80, together with a series resistor 90, is connected in parallel to the heating element 10. The glow lamp 80 illuminates when the external power switch 7 in the form of the thermostat of the iron soleplate is switched on provided that the internal power switch 6 is closed. Hence, glow lamp 80 indicates whether a voltage is applied to the heating element 10 or not. Commonly, glow lamp 80 and associated dropping resistor 90 are provided outside the electronic assembly 1. In case of the above mentioned steam iron of Bosch, the glow lamp 80 is provided in the rear left portion of the grip handle. As indicated in dashed lines, the glow lamp can also be mechanically integrated into the electronic assembly 1.
As known, glow lamps are very sensitive to climatic changes. Furthermore, glow lamps can only be energized from the line voltage via a high-resistance dropping resistor. Even in case the glow lamp would be replaced by a light-emitting diode being energized by means of the low voltage power supply of the electronic assembly it would be necessary to provide a voltage tap between the external power switch 7 and the heating element 10.
It is a general object of the invention to provide a reliable and low-priced device for detecting, monitoring and controlling the operating status of an electric iron.
According to a first aspect, the invention provides a device for detecting, monitoring and controlling the operating status of an electric iron which is provided with at least one electric heating circuit having a heating element and a first power switch of the iron connected in series to the heating element. The device includes a control unit being provided as an integrated circuit. A second power switch which is controlled by the control unit depending on the operating status of the electric iron is connected in series with the electric heating circuit. An indicator unit having at least one optical indicator element indicates the heating status of the electric iron. A low voltage power supply energizes at least one of the above units. A low-impedance measuring resistance is connected in series with second power switch, and provides an indirect detection means for the switching status of both power switches. The device further includes means for supplying a voltage drop arising at the measuring resistance as an input signal to the control unit for evaluating the input signal, and means for supplying a control signal to the indicator unit for indicating a present heating status of the electric iron by means of the indicator unit.
Accordingly, the inventional device avoids the common series connection of a glow lamp and resistor in parallel to the at least one heating element. In addition, the wiring in the form of a voltage tap xe2x80x9cbehindxe2x80x9d the thermostat i.e. between the first power switch and the heating element is avoided. By means of detecting a voltage drop on the measuring resistance the switching status of the first or thermostatic power switch of the iron and of the second or internal power switch of the electronic assembly, as well as, the heating status of the electric iron and its heating element(s) are indirectly detected. Therefore, the heating status of the electric iron and its heating element(s) can be indicated by an indicator element of the indicator unit. This solution is a low-cost solution but nevertheless very reliable and any break and malfunction of the heating element can be detected. In contrast thereto, the glow lamp 80 of FIG. 1 indicates a voltage even in case of a current interruption within the heating element 10 itself and thus falsely indicates supply of energy to the heating element.
Furthermore, the measurement of the current through the low-impedance measuring resistance allows a more refined analysis of the present status of the electric iron. For example, the control unit of the electronic assembly can detect by analyzing the current value of the measured heating current whether or not a plurality of heating elements connected in parallel to one another operate correctly. It is also possible to detect a failure of the second or internal power switch controlled by the control unit. Likewise, the control unit can check and monitor a safety shut-off function effected by the internal power switch. In addition to taking into account the measured heating current, the control unit can analyze any sensor signals and/or timing signals supplied thereto or generated therein and can produce correspondingly adapted control signals for controlling the indicator unit and/or the internal power switch of the electronic assembly.
According to a further aspect, the above mentioned indicator element is provided for indicating that a heating current is flowing through the at least one heating element. Hence, the indicator element performs the function of the glow lamp 80 of FIG. 1 without the disadvantages of this prior art embodiment. The indicator element, preferably a light-emitting diode, constitutes a cost and space saving solution for providing a user with the common visual light signal appearing when the electric iron has been plugged in and disappearing when the electric iron has reached a temperature called for by the thermostatic power switch.
According to an alternative embodiment the indicator element is provided for indicating that the desired operating temperature of the iron has been reached only after a predetermined number of ON/OFF-switching cycles have been counted in the form of voltage drop cycles on the low-impedance measuring resistance. Thus, the user starts ironing only after utilizing the full heat capacity of the iron sole.
According to a further aspect, an amplifier is provided for amplifying the voltage drop on the low-impedance measuring resistance. The amplifier is preferably provided in the integrated control unit. In a preferred embodiment, the control unit is implemented in form of a single integrated circuit, preferably provided in form of an application specific integrated circuit (ASIC). Preferably, the inventive low-impedance measuring resistance is provided within the electronic assembly and a voltage tap of the resistance is connected to a signal input of the amplifier integrated in the control unit.
The impedance value of the low-impedance measuring resistance is preferably selected such that the dissipated power is lower than 1 Watt and preferably not higher than 0.5 Watt at the maximum possible value of the heating current. Accordingly, the impedance value should be lower than 4 mOhm at a maximum heating current flow of 16A.
According to a further aspect, the inventive low-impedance measuring resistance, on its one connection side, is connected to ground and, on its other connection side, is connected to a measuring signal input of the integrated control unit. Preferably, the low-impedance measuring resistance is formed by a section of a heating current conductor path of the electronic assembly. In this manner, the heating current measurement can be implemented with a minimum of additional electronic connections and nearly without warming up the circuit board of the electronic assembly in an undue manner.
Furthermore, it was confirmed that the additional function of evaluating the measured voltage drop on the low-impedance measuring resistance does not impair the performance of the IC circuit, for example, its conversion function.
According to a further aspect of the inventional device, an additional input to the control unit comprises one or more signals generated by one or more sensors sensing position and/or movement of the electric iron in order to shut-off the heating current via the internal power switch whenever the electric iron has not been manipulated over a predetermined time period.
According to a further aspect of the inventional device, an input to the control unit can be a signal generated by a timer in order to shut-off the electric heating circuit via the second power switch when a predetermined considerably long time period has elapsed after the first power switch has been initially switched ON. This time period can be monitored by the inventional sensing of the voltage drop on the measuring resistance and it is, for example, possible to detect, by analyzing the ON/OFF-switching time pattern of the first power switch, that the electric iron has not been manipulated over the predetermined time period. If a user forgets to disconnect the iron from the line voltage supply the heating current is automatically shut-off after one hour or the like which constitutes a time period being longer than usual interruptions during ironing. Of course, any timers can be implemented within the control unit itself.
The invention is mainly implemented by the electronic assembly. Preferably, this assembly is designed in form of an integrated module or unit. Preferably, it has only two terminals to connect it in series with the heating circuit apart from a connection to the line voltage supply for energizing the low voltage power supply integrated within the electronic module.
A preferred embodiment of the invention will now be described referring to the attached drawings.